Sensors, such as, for example, optical sensors exemplarily comprising LEDs or photodiodes, are more frequently implemented in special package technologies to allow a light wave or light beam easy entry to a sensor element in the package. Acoustic sensors, too, such as, for example, microphones, where an acoustic wave is to impinge on a sensor element with the least interference possible, or pressure sensors where a pressure or pressure change is to propagate to a sensor element in a package with the least interference possible are also implemented in special package technologies.
An article by M. Müllenborn et al. at EUROSENSORS XIV, Aug. 27 to 30, 2000, Copenhagen, Denmark, discusses a setup of stacked silicon microphones. In the stacked silicon microphones, a microphone chip is deposited “head first” on a carrier chip serving as the substrate. The contacts of the microphone chip here are arranged on a surface of the microphone chip looking away from the carrier chip. Subsequently, an interconnect chip is deposited on the microphone chip by means of chip-to-wafer bonding or wafer-to-wafer bonding. The interconnect chip comprises a recess through which an acoustic wave may propagate. After that, an ASIC (application-specific integrated circuit) processing the signals from the microphone chip is deposited on the interconnect chip for example by means of chip-to-wafer bonding. In addition, a sound inlet pipe is deposited on the interconnect chip so that a sound wave may propagate from the surroundings through the recess in the interconnect chip to a membrane on the microphone chip. The setup generated in this way is finally sprayed with a conductive polymer so that the shielding formed in this way creates mechanical protection and electromagnetic shielding.
However, it is of disadvantage with this method of manufacturing where the silicon chips are deposited “head first” on a carrier substrate that the contacts thereof are arranged on a surface looking away from the carrier chip so that the manufacturing costs are very high. With these so-called chip-size packages manufactured by means of chip bonding, the silicon chips themselves form the package and the positions of the contacts on the chips and the positions of the vias in the interconnect chip and thus the layout need to be adjusted individually for every type of microphone implemented.
This is why the developing costs for a stacked silicon microphone are very high and a microphone implemented in this way has very low flexibility in its package design or layout of the package dimensions. The microphone chip and the interconnect chip must be adjusted, as far as the layout is concerned, individually for every electrical apparatus making use of such a microphone and making special requirements to the dimensions of the microphone.
WO 02/45463/A2 shows a micromechanical silicon microphone the package of which is produced using a substrate in combination with a lid. The substrate here serves as a carrier or carrier substrate for one or several silicon chips, whereas the lid shields the device from the surroundings. An opening is provided in the substrate or the lid as a sound inlet. A silicon-capacitor microphone and an amplifier chip are positioned in the package formed in this way.
An article by J. Bergqvist and F. Rudolf at Sensors and Actuators, A45, 1994, on pages 115-124, deals with silicon-capacitor microphones employing bond technologies and backside etching technologies. Thus, a microphone chip having a pressure-sensitive membrane and an acoustically transparent back plate is arranged in a package. The package consists of a conductive circuit board having a pressure inlet and a metal cap.
Disadvantages of silicon-capacitor microphones implemented in this way are the increased demand of material for the lid and the carrier substrate or printed circuit board and the increased demand of space making a flexible usage of the microphone difficult in applications critical as to space. Several process steps may be executed in parallel with this concept, but nevertheless protecting the silicon chip or silicon microphone entails increased complexity and costs since this is frequently performed in two method steps. The structures susceptible to corrosion are at first cast, and subsequently a lid is deposited as a protection against mechanical influence.
DE 103 03 263 A1 shows a sensor module. The sensor module consists of a microphone chip arranged in a package which is formed of a package lid and a carrier material. The package is deposited on a printed circuit board by means of a solder connection. In the carrier material, the package has a sound inlet opening opposite a hole in the printed circuit board.
This setup of a sensor module, too, has the disadvantages of a high demand of material for the printed circuit board and the lid, increased processing complexity and increased demand of space for the microphone implemented in this way.
An article by Dr. M. Füildner and Dr. A. Dehè at zwölfte GNA/ITG-Fachtagung Sensoren und Messsysteme 2004, Ludwigsburg, March 2004, having the title “Mikromechanische Silizium-Mikrophone” deals with silicon microphones. The conventional sensor modules or silicon microphones discussed there exhibit SMD demonstrators accommodated on a through-contacted FR4 substrate having a molded cap or cap produced by means of an injection molding process or in a premold hollow package. The sound inlet here is via a hole on the bottom or in the FR4 substrate.
Again, is it of disadvantage with this setup of the conventional sensor module that depositing materials, such as, for example, connective materials, casting compounds or the lid, is performed individually for each device or each sensor module during manufacturing, resulting in increased manufacturing costs. In addition, the package is produced in a complicated manner by depositing a lid on a substrate or printed circuit board.
Packages having a lid with a sound hole additionally are of disadvantage in that an acoustic resonator will form. Similarly to the spring-and-mass principle in mechanics, the sound hole may be considered to be an acoustic mass and the volume behind it, i.e. the volume in the package between the substrate and the lid, may be considered to be an acoustic spring. The bandwidth of the microphone is reduced or limited by forming this resonator. At the same time, the demand of space for a microphone embodied in this manner is increased, since a minimal size is determined by reservations or tolerances or a distance from the chips to the lid and a minimal width or thickness of the lid.